1. Field of the Invention
This invention relates to a paper feed system where a plurality of papers placed on a paper feed table are taken out and transferred one by one by a first paper feed mechanism and delivered to an image forming section by a second paper feed mechanism at a predetermined time.
2. Description of the Related Art
There have been proposed various paper feed systems to be installed in printers such as ink jet printers and stencil printers.
In such a paper feed system, generally, a plurality of papers placed on a paper feed table are taken out one by one by a pair of rotating paper feed rollers, transferred to a resist roller and delivered by the resist roller to an image forming section comprising a line head which discharges the ink and a printing drum.
In such a paper feed system, in order to overcome the problem of inclination of the papers due to an oblique feed of the papers in the paper transfer step, the paper feed rollers are kept rotated for a while even if the leading edge reaches the resist roller before the resist roller is started to be rotated. Accordingly, in such a paper feed system, the paper transferred from the paper feed table to the resist roller is sagged in the direction of transfer between the paper feed rollers and the resist roller while the resist roller transfers it in the image forming section. By suitably sagging the papers in this manner, the inclination of the papers due to an oblique feed of the papers in the paper transfer step can be overcome.
In such a conventional paper feed system, the paper feed rollers are generally connected to a driving source by way of an electromagnetic clutch, and the electromagnetic clutch is engaged each time one paper is taken out to permit the paper feed rollers to rotate by a predetermined angle.
Further, for example, if paper feed rollers are driven to rotate for only a predetermined angle even when the printing speed differs at an image forming section, faults will arise in paper feed and conveyance. Taking this fact into consideration, Japanese Unexamined Patent Publication No. 10(1998)-035910 proposes a paper feed apparatus in which the angle for which the paper feed roller is driven to rotate is varied, according to the printing speed at an image forming section.
In such a paper feed system, the waiting positions of the papers fluctuate depending on the manner in which the papers are set on the paper feed table 11 as shown in FIG. 4. In normal use, the fluctuation in the waiting positions of the papers is about 15 mm on the upstream side and cannot be defined on the downstream side depending on the degree of the feed of superimposed papers. Accordingly, there is a probability that the waiting positions of the papers fluctuate in the range shown by the arrow in FIG. 5. When the printing papers different from each other in waiting position are transferred in the same manner, the amount of the sagging cannot be uniform and the paper supply timing to the image forming section differs from paper to paper, whereby the position of the image formed by the image forming section is shifted.
Though taking into account the printing speed in the image forming section, the paper feed system disclosed in Japanese Unexamined Patent Publication No. 10(1998)-035910 does not take into account the fluctuation in the waiting positions.